The invention relates to a process for galvanizing limited areas of conductive surfaces or surfaces which have been made conductive by depositing a metal or metal alloy from an electrolytic solution.
Processes of this type have already become known. They usually are based on two fundamental principles. The parts to be galvanized are either contacted with the electrolyte only at the desired spots while dipping into an electrolytic bath. This contact can for instance be obtained by use of rollers (West German Pat. No. 186,654), wheels (West German Pat. No. 2,324,834) or open hollow spaces (West German Pat. No. 1,807,481). Another process makes use of the conventional baths but modifies the metal ion supply and the electrical field distribution at the surface to be treated by interposition of for instance shields (West German Pat. No. 2,263,642), cover devices (West German Pat. No. 2,362,489), electrically isolated rims moving on rollers (West German Pat. No. 2,009,118), baskets (West German Pat. No. 2,230,891l ), or lacquer coatings (West German Pat. No. 2,253,196).
These prior processes have the shortcoming that they permit only deposits of more or less uniform coating thicknesses. However, in order to improve the functional properties of technical surfaces such as in plug or switch contacts it is desirable to have a thick coating only in the immediate contact area while for the remaining surface a thinner coating is sufficient as corrosion protection. The transition between the different coating thicknesses in this case should be even and in case of plug and switch contacts these should for instance be a lenticular distribution of thicknesses in the contact area.
Further shortcomings of the prior art are that either there is only an unsatisfactory metal ion supply which results in a deficient metal coating, or they are rather expensive and time- and material-consuming since the necessary covering must first be installed and then again be removed and masks must be renewed after certain periods of time because of wear and tear.
It is therefore an object of the present invention to provide for a process for galvanizing limited areas of conductive surfaces or surfaces that have been made conductive by means of deposit of metal or metal alloys from electrolytic solutions in which the shortcomings of the prior art processes are avoided and in which in particular a distribution of coating thicknesses is obtained so as to comply with the function of the article.